Method for tone-mapping a video sequence

Abstract

The present invention generally relates to a method and device for tone-mapping a video sequence in which a local tone-mapping operator is applied on each frame of the video sequence to be tone-mapped. The method is characterized in that the spatial neighborhoods used by said local-tone-mapping operator are determined on a temporal-filtered version of the frame to be tone-mapped.

1 - 9 . (canceled) 
     
     
         10 . Method for tone-mapping a video sequence in which a local tone-mapping operator is applied on each pixel of each frame of the video sequence to be tone-mapped, characterized in that the spatial neighborhoods defined around the pixels to be tone-mapped and used by said local-tone-mapping operator are determined on a temporal-filtered version of the frame to be tone-mapped. 
     
     
         11 . Method according to  claim 10 , wherein the method comprises
 obtaining a motion vector for each pixel of the frame to be tone-mapped, and   motion compensating some frames of the video sequence using the estimated motion vectors and temporally filtering the motion-compensated frames to obtain the temporal-filtered version of the frame to be tone-mapped.   
     
     
         12 . Method according to the  claim 11 , wherein the method further comprises
 detecting non-coherent motion vectors and temporally filtering each pixel of the frame to be tone-mapped using an estimated motion vector only if this motion vector is coherent, a motion vector being detected as being non-coherent when an error (ε n (x,y), ε b,n (x,y), ε f,n (x,y)) between the frame to be tone-mapped and a motion-compensated frame corresponding to this motion vector is greater than a threshold.   
     
     
         13 . Method according to  claim 12 , wherein a length N of a temporal filter is obtained, motion-compensated frames are obtained through motion-compensation of the current frame in regard to the frame to be tone-mapped thanks to the estimated motion vectors and the temporal-filtered version of the frame to be tone-mapped) then results from the temporal filtering of said motion-compensated frames using said temporal filter. 
     
     
         14 . Method according to  claim 12 , wherein a dyadic wavelet decomposition is applied on the frame to be tone-mapped to build a pyramid where each level corresponds to a low frequency frame belonging to either a forward or backward part, each low frequency subband of each part being computed by using:
 a motion prediction step in the course of which a frame H t+1  is obtained from the difference between a reference frame F t+1  and a backward or forward motion-compensated version of a current frame Ft; and   an update step in the course of which a low frequency frame L t  belonging to either a forward or backward part is obtained by adding the frame F t  with the inverted-motion-compensated version of the frame H t+1 ,   for each pixel of the frame to be tone-mapped, at least one low frequency frame of the backward part is selected and at least one low frequency frame of the forward part are selected and the pixel of the temporal-filtered version of the frame to be tone-mapped is a blending of the two pixels belonging to the two selected low frequency frames.   
     
     
         15 . Method according to the  claim 15 , wherein starting from the lowest frequency subband of the backward and the forward parts of the decomposition, all the low frequency subbands of the decomposition are considered and a single low frequency subband is selected for each pixel of the frame to be tone-mapped when the corresponding motion vector is coherent. 
     
     
         16 . Device for tone-mapping a video sequence comprising a local tone-mapping operator, wherein it further comprises means for obtaining a temporal-filtered version of a frame of the video sequence to be tone-mapped and means for determining the spatial neighborhoods defined around the pixels to be tone-mapped and used by said local-tone-mapping operator. 
     
     
         17 . Device according to the  claim 16 , wherein it further comprises means configured to implement one of the method according to  claim 10 .